The use of radio communication networks is rapidly becoming a part of the daily life for more and more people around the globe. For instance, the GSM (Global System for Mobile Communications) networks offer a variety of functions. Generally, radio communication systems based on such networks use radio signals transmitted by a base station in the downlink over the traffic and control channels are received by mobile or portable radio communication terminals, each of which have at least one antenna. Historically, portable terminals have employed a number of different types of antennas to receive and transmit signals over the air interface. In addition, mobile terminal manufacturers encounter a constant demand for smaller and smaller terminals. This demand for miniaturization is combined with desire for additional functionality such as having the ability to use the terminal at different frequency bands, e.g. of different cellular systems, so that a user of the mobile terminal may use a single, small radio communication terminal in different parts of the world having cellular networks operating according to different standards at different frequencies.
Further, it is commercially desirable to offer portable terminals which are capable of operating in widely different frequency bands, e.g., bands located in the 800 MHz, 900 MHz, 1800 MHz, 1900 MHz and 2.0 GHz regions. Accordingly, antennas which provide adequate gain and bandwidth in a plurality of these frequency bands are employed in portable terminals.
Several attempts have been made to create such antennas. The general desire today is to have an antenna, which is positioned inside the housing of a mobile communication terminal. The most common built-in antennas currently in use in mobile phones are the so-called planar inverted-F antennas (PIFA). This name has been adopted due to the fact that the antenna looks like the letter F tilted 90 degrees in profile. Such an antenna needs a feeding point as well as a ground connection. If one or several parasitic elements are included nearby, they can be either directly coupled to ground or connected to ground via a matching impedance, capacitive coupling, etc. The height of the PIFA antennas is often a limiting factor for decreasing the size of the mobile communication terminal. The geometry of a conventional PIFA antenna includes a radiating element, a feeding pin for the radiating element, a ground pin for the radiating element, and a ground substrate commonly arranged on a printed circuit board (PCB). Both the feeding pin and the ground pin are necessary for the operation of such an antenna, and are arranged perpendicular to the ground plane, wherein the PIFA radiating element is suspended above the ground plane in such a manner that the ground plane covers the area under the radiating element. This type of antenna, however, generally has a fairly small bandwidth in the order of 7% of the operating frequency. In order to increase the bandwidth for an antenna of this design, the vertical distance between the radiating element and the PCB ground may be increased, i.e. the height at which the radiating element is placed above the PCB is increased. This, however, is an undesirable modification as the height increase makes the antenna unattractive for small communication devices and may reduce directivity.
U.S. Pat. No. 6,456,250 discloses a multi frequency band antenna with a low band portion tuned to a low frequency band, a first high band portion tuned to a first high frequency band at higher frequencies than the low frequency band, and a separate, electrically coupled second high band portion that is tuned to a second high frequency band at a higher frequency than the low frequency band and different from the first high frequency band. The low band portion and the first high band portion have a common first grounding point, a common feeding point, and a first conductor portion, which forms part of the low band portion and of the first high band portion. The first conductor portion is electrically connected to the first grounding point and to the common feeding point. The second high band portion is coupled to the first conductor portion. An embodiment of the antenna disclosed in U.S. Pat. No. 6,456,250 is tuned to the frequencies 900 MHz (GSM band), 1800 MHz (DCS band) and 1900 MHz (PCS band).
However, it is desirable to achieve a high gain antenna supporting a single low-band and a wider range of multiple high-bands. It is also desirable to achieve equivalent performance in a smaller volume, which allows for smaller, more attractive phones.
Hence, an improved a multi-band radio antenna device having a wide high-bandwidth would be advantageous. In particular a multi-band radio antenna device allowing for increased efficiency with regard to e.g. size, cost, bandwidth, design flexibility and/or radiation efficiency of the multi-band radio antenna device would be advantageous.
The antenna structure of such an advantageous antenna device is advantageously suitable for built-in antennas, at the same time having a wide high-frequency band bandwidth, which enables the antenna to be operable at a plurality of frequency bands, and having a high efficiency.
More specifically, an antenna with high-gain at high-band would be advantageous, which is both small and has good performance not only in a low frequency band, such as the 900 MHz GSM band, but also good performance in several higher frequency bands, such as the 1800 MHz GSM or DCS band, the 1900 MHz GSM or PCS band, and the 2.1 GHz UMTS band.